This invention relates to methods and apparatus for scavenging and using energy caused by changes in pressure. This includes but is not limited to using changes of pressure in closed or substantially closed atmosphere environments to create electrical energy which is then used as a power source.
The invention will be described in reference to pneumatic devices and in particular pneumatic tires used in vehicles. However, this description is one exemplary embodiment of the invention and systems and methods of the invention are applicable to any circumstance where changes in pressure occur at a frequency that they may be used to convert mechanical energy to electrical energy.
Tire safety studies show that maintaining proper tire pressure improves vehicle handling, improves fuel economy, increases tire life and helps avoid accidents. An NHTSA research survey of U.S. passenger vehicles found that 27% of passenger cars on U.S. roadways were driven with one or more substantially under-inflated tire. The survey found that 33% of light trucks (including sport utility vehicles, vans and pickup trucks) are driven with one or more substantially under-inflated tire. Other studies have shown that nearly 20% of service stations providing customers with tire pressure gauges on their air pumps use gauges that over report the pressure present in a tire by at least 4 psi (pounds per square inch) or more. At pressure levels that are typical for most passenger cars or SUVs, nearly 10% of service station air pump gauges over report by 6 psi or more. In addition, radial tires can lose much of their tire air pressure and still appear to be fully inflated.
In response to this safety issue, the federal government has enacted standards which require motor vehicles to become equipped with tire pressure monitoring systems. The standards specify performance requirements for tire pressure monitoring systems to prevent significant under-inflation of tires and the resulting safety problems. The standard applies to passenger cars, multipurpose passenger vehicles, trucks and buses that have a gross vehicle weight rated of 10,000 pounds or less. The tire pressure monitoring system refers to a system that detects when one or more of the vehicles tires are under-inflated and illuminates a low tire pressure warning telltale. The low tire pressure warning telltale must be mounted inside the occupant compartment in front of and in clear view of the driver. The tire pressure monitoring system must continue to meet the requirements of the standard when the vehicle's original tires are replaced with tires of any optional or replacement size.
Related art tire pressure monitoring systems provide vehicles using pneumatic tires with a system having a sensor to sense conditions of a tire. See U.S. Pat. Nos. 6,438,193 and 6,518,877 which are hereby incorporated by reference. The conditions may include internal pressure, temperature, number of revolutions, etc. Related art systems are mounted in the tire and include a transmitter which communicates sensed data to a receiver located in the vehicle. The sensed data may then be communicated to the vehicle operator via a user interface, such as a display. The related art systems are often powered by batteries which wear out and need to be replaced. This increases labor costs and hazardous waste. This may also result in system failures due to lack of power during the operation of the vehicle.